Absorption refrigeration systems are well known to the art. The basic principle of those systems is identical to that of the single-stage compression system except for the manner in which the pressure of the refrigerant vapor is increased to the level required for condensation. In particular, the compressor of the compression system is replaced by the absorber and the generator of the absorption system. Instead of compressing a low-pressure refrigerant vapor, it is first absorbed by a weak solution of the refrigerant and is thereafter pumped into a generator where it is heated. The heating process boils the refrigerant vapor from the solution and directs it, at high pressure, to the condenser.
Absorber heat exchange ("AHE") cycles are known to be useful in absorption refrigeration chillers. In principle, all AHE cycle absorption chillers exchange heat of absorption from the absorber to the generator--thereby reducing the amount of heat required by the generator. Typically, AHE equipment not only transfers the heat of absorption to the generator or to the strong solution before it enters the generator, but also takes advantage of the fact that the weak solution is already hotter than the strong solution which is formed, and additionally transfers some of that heat differential.
Generator absorber heat-exchange ("GAX") cycles are known to be an improvement to AHE cycle systems. In a GAX cycle machine, the heat of absorption is transferred at a temperature above the boiling point of the strong refrigerant solution, thereby maximizing the temperature overlap between the absorber and the generator and more efficiently transferring heat between the two components.
In both AHE and GAX cycle machines, heat transfer may occur by providing an additional heat-exchange pathway into the circuit followed by the refrigerant fluid, or it may be done by providing a separate work fluid in a separate circuit to transfer heat between the absorber and the generator. To briefly describe an absorption chiller with an integrated AHE pathway, a generator heats an absorbent solution, preferably ammonia/water, so as to release the refrigerant, ammonia in vapor form, from solution as previously described. The refrigerant vapor then passes through an analyzer to a rectifier and then to a condenser where it is condensed at a relatively high pressure by the ambient air or by fluids such as water or water/glycol mixtures. The condensed ammonia passes through a pressure reduction device and a refrigerant heat exchanger to an evaporator where the pressure is further reduced and the refrigerating effect is accomplished. The low pressure vapor then flows back through the refrigerant heat exchanger to a solution absorber heat exchanger where it comes into contact with a weak solution of refrigerant fluid flowing from the generator. In the absorber heat exchanger the weak solution absorbs a portion of the low pressure vapor with the resulting solution passing into an absorber cooled by ambient air or by fluids such as water or water/glycol mixtures. This results in the remaining ammonia vapor being absorbed in the absorbent solution. The strong solution thus formed passes through a solution pump, to help overcome the difference between the low pressure and the high pressure sides of the system, to the rectifier, the absorber heat exchanger and the generator, where the cycle repeats itself. This type of single effect cycle system has a fuel based system C.O.P. of approximately 0.5.
The generator absorber heat exchange cycle (GAX) operates at the two pressure levels of the single effect absorber heat exchange (AHE) cycle. The difference between the GAX cycle and the AHE cycle is that the GAX cycle recovers additional absorption heat from the high temperature end of the absorber and transfers it to the cooler low temperature end of the generator by generating vapor with the additional heat thereby reducing the heat input required from external sources. The temperature of the strong solution in the cold end of the generator must be such that the temperature of the weak solution in the hot end of the absorber is at a high enough temperature for heat transfer to occur in the GAX cycle. The greater the temperature overlap the greater amount of heat that can be transferred to the generator.
Although known GAX cycle absorption machines have acceptable efficiencies, they may be expensive to manufacture and operate. Particularly, many prior art GAX systems require an additional GAX pump and a second work fluid to transfer heat from the absorber to the generator. A need therefore exists for an economical GAX cycle absorption machine that does not require a second work fluid or its associated pump. The present invention addresses that need.